The present invention relates to an improvement of the hydraulic control system for an automatic transmission gear to prevent shocks frequently caused when the mechanism is shifted to the 4th speed.
Various types of automatic transmission gears have been used to drive a secondary mover while keeping the output torque and the revolution rate of the prime mover in an internal combustion engine or the like at predetermined values. Hydraulic control systems are often used for controlling such automatic transmission gears.
Hydraulic control systems are used for controlling the automatic transmission gears in an automobile. In an automatic transmission gear of 4-speed advance type comprising 3 pairs of clutches including a friction clutch which is hydraulically driven to connect an input shaft with a carrier of Ravigneawx type planet wheel gears for the 4th speed, 2 pairs of brakes and one pair of oneway clutches, it is necessary to engage 2 pairs of clutches for the 3rd speed whereas for the 4th speed it is necessary to engage one pair of brakes with the friction clutch which is different from the one for the 3rd speed. It therefore is extremely difficult to set the timings for releasing the 2 pairs of clutches which have been engaged for the 3rd speed and newly engaging friction clutch with one pair of brakes for the 4th speed as well as to set the initial engagement torque, thereby causing transmission shocks or affecting the durability or the strength of clutches, brakes, etc.